Concrete blocks, also referred to as concrete masonry units (CMU's), are typically manufactured by forming them into various shapes as part of an automated process employing a concrete block machine. Such machines typically employ a mold frame assembled so as to form a mold box, within which a mold cavity having a negative of a desired block shape is formed. To form a block, a pallet is moved by a conveyor system onto a pallet table, which is then moved upward until the pallet contacts and forms a bottom of the mold cavity.
The mold cavity is then filled with concrete and a head shoe assembly is positioned to form a top of the mold cavity. The head shoe assembly then compresses the concrete (typically via hydraulic or mechanical means) to a desired psi rating (pounds-per-square-inch) while simultaneously vibrating the mold cavity along with the vibrating table. As a result of the compression and vibration, the concrete reaches a level of “hardness” which enables the resulting finished block to be immediately removed from the mold cavity. To remove the finished block, the mold frame and mold cavity remain stationary while the shoe assembly, pallet, and pallet table move downward and force the finished block from the mold cavity. The conveyor system then moves the pallet bearing the finished block away and a clean pallet takes its place. This process is repeated for each block.
For many types of CMUs (e.g. pavers, patio blocks, light-weight blocks, cinder blocks, etc.), retaining wall blocks and architectural units in particular, it is desirable for at least one surface of the block to have a desired texture, such as a stone-like texture, for instance. When arranged to form a structure with the textured surface visible, the structure will have the appearance of being constructed from natural stone.
One technique for creating a desired texture on a block surface is to provide a negative of a desired texture or pattern on a moveable side wall of the mold cavity. During the manufacturing process, the side wall is moved to an extended position to form the mold cavity. As described above, the mold cavity is then filled with concrete and compressed/vibrated. The side wall is then moved to a retracted position and the finished block, as described above, is forced from the mold cavity and onto the pallet by the head shoe assembly. The finished block, including a surface having the desired texture, is then transported on the pallet by the conveyor for curing.
While such a technique is effective at forming a textured surface, air pockets trapped between the textured surface of the moveable side wall and concrete fill are forced out during the compression/vibration process, causing the concrete to settle proximate to the textured surface and resulting in the finished block having a height along the textured surface (e.g. front face of block) which is shorter than that along an opposite surface (e.g. rear face of block). Consequently, unless compensated for in some fashion, a structure (e.g. a retaining wall) will tend to have an undesirable lean in a direction toward the textured surface.